Scepter x20wg screen problems

[Fredrow]

I have a Scepter x20wg with problems of the screen going black, but then the front LEDs stay blue. So the LEDs are telling me that the x20 is still seeing an incoming signal from my PC. So after doing some research and looking around on the circuit board, I did discover some bad caps (which I replaced) I also noticed some board discolor around the 2 MOSFET ICs on the bottom of the board (so I just went ahead and replaced them too) But I'm still having the same problem, the screen only stays on for about 30s then goes black and the front LEDs are still blue.

Any ideas?

I'm going to just go ahead now and upload pics of the bottom and top of the circuit board, just because after reading through these forums that seems to be the first response back is asking for pics. (As you will notice from the pics on the bottom of the board the two jumper wires are there because I ruined the landing on one leg of the IC connections)

[PlainBill]

Re: Scepter x20wg screen problems

I have a Scepter x20wg with problems of the screen going black, but then the front LEDs stay blue. So the LEDs are telling me that the x20 is still seeing an incoming signal from my PC. So after doing some research and looking around on the circuit board, I did discover some bad caps (which I replaced) I also noticed some board discolor around the 2 MOSFET ICs on the bottom of the board (so I just went ahead and replaced them too) But I'm still having the same problem, the screen only stays on for about 30s then goes black and the front LEDs are still blue.

Any ideas?

I'm going to just go ahead now and upload pics of the bottom and top of the circuit board, just because after reading through these forums that seems to be the first response back is asking for pics. (As you will notice from the pics on the bottom of the board the two jumper wires are there because I ruined the landing on one leg of the IC connections)

The problem is referred to as the 'Two seconds to black' problem. One day Real Soon Now :roll: I'll write up a detailed explanation of how to troubleshoot it.

Note the picture I defaced. The first step requires a DMM. Set it to the 2K ohm scale and with the power off to the monitor measure the resistance between A and A'. Then measure the resistance between B and B'. What are the readings (as accurately as possible)?

PlainBill

[Fredrow]

Re: Scepter x20wg screen problems

After testing both spots (A to A') and (B to B') I got the exact same reading on both which was 623 ohms.

[PlainBill]

Re: Scepter x20wg screen problems

After testing both spots (A to A') and (B to B') I got the exact same reading on both which was 623 ohms.

The good news is that it is not a transformer. The bad news is that we must try to identify the bad component. The good news is that the transformers can be difficult to locate. The bad news is that now we get into tests that involve high voltage and enough current to hurt you.

FIRST, one more safe test. What is the resistance from A to B on the attached picture? (Measure with monitor unplugged).

A little background. The inverter controller in this monitor first turns on all CCFLs at full brightness. After a fraction of a second it reduces the drive to normal levels and monitors the voltage across and current through each CCFL. If any of these are out of the proper range, the controller shuts down the inverter.

The following tests will be done with the monitor operating. Both the AC supply (120 VAC in the US; 240 VAC in some countries) are enough to hurt you. The rectified line voltage (1.4 times as high as AC supply) will also give you quite a jolt. As long as you aren't doing something foolish such as working in a damp basement while sitting on a metal chair and holding onto a cold water pipe with one hand it's unlikely to be fatal. The inverter output also has enough voltage and current to hurt. So be careful. I recommend having an assistant who will press the power button on the monitor while you hold the probes

There are eight readings to take. I've marked points V1 through V4 (the voltage sense lines) and R1 through R4 (the current sense lines). I have also identified a ground point.

The process goes like this. Set the meter to the 20 VAC range. Black probe goes to Gnd, red to the point under test. The assistant pushes the power button, the CCFLs go on, you get the reading, the CCFLS go off, the assistant presses the power button again TWICE, the CCFLs come on again, you verify the reading and write them down. Repeat for the other 7 test points.

The 4 Vx test points should read approximately the same, the 4 Rx should also read fairly close together.

PlainBill

[Jules3084]

Re: Scepter x20wg screen problems

Hello,

Can anyone help me please? This is a Sceptre X20WG-Naga monitor.

I found this thread from the search, and I have the same problem, just that the screen would only show (dim) for a second or so.

I don't know what happened with the previous persons problem.

I have also changed all the caps and the two surface mount MOSFET 4511GM
drivers. Still no change.

Following PlainBill's instructions and pictures, I made power off measurements.
A to B is open
A to A' is 617 ohms
B to B' is 619 ohms
R1 to R2 is 15.12K ohms
R3 to R4 is 15.09K ohms

I'll try making the power on measurements tonight, unless directed otherwise.

Thank you

[retiredcaps]

Re: Scepter x20wg screen problems

I'll try making the power on measurements tonight, unless directed otherwise.

Please post pictures off your boards following the links/instructions in PlainBill's signature.

Your board could be slightly different or have different characteristics.

Also, do you have another working LCD?

[Jules3084]

Re: Scepter x20wg screen problems

Pictures of the Sceptre X20WG inverter board are attached.

Yes I'm am using a spare LCD monitor on the computer now,
but it is a older Hitachi.

[retiredcaps]

Re: Scepter x20wg screen problems

I have the same problem, just that the screen would only show (dim) for a second or so.

Okay, let's get a bit more detail/clarification.

Hookup a computer and boot it so that it displays something.

1) If you connect the x20wg, do you see the screen flash briefly and then go to black?

2) Do you see the display if you shine a flash light on the LCD?

The older Hitachi might come into play in helping testing out the ccfls.

[Wrog]

Re: Scepter x20wg screen problems

Pictures of the Sceptre X20WG inverter board are attached.

Interesting... did you replace C101 (center topside, below and to the right of the big arrow) with a poly cap instead of an electrolytic?

[Jules3084]

Re: Scepter x20wg screen problems

I boot up on a spare machine, and the X20WG flashes for a second,
each time, shortly after the monitor is turned on. While this is done,
I can see the current state of the computer, then its black until I shut off the monitor and turn it back on again. Then it will flash again for a second.

I tried shining a flashlight on the front screen at different angles but I can't
see anything other than black. I'm not sure if I am doing it right.

Yes, the electrolytic C101 was replacxed with a poly cap. The one
that was in there had the top cap expanded. I thought it would be a better
cap since it has higher ripple current rating than a standard electrolytic.

[retiredcaps]

Re: Scepter x20wg screen problems

I boot up on a spare machine, and the X20WG flashes for a second,
each time, shortly after the monitor is turned on. While this is done,
I can see the current state of the computer, then its black until I shut off the monitor and turn it back on again. Then it will flash again for a second.

What you are experiencing sounds like 2 seconds to black. More below.

Yes, the electrolytic C101 was replacxed with a poly cap. The one
that was in there had the top cap expanded. I thought it would be a better
cap since it has higher ripple current rating than a standard electrolytic.

For all the people reading this in the future, this is an excellent example why we request pictures of *your* particular board. Some people are lazy and say "it looks like the board in post xx", while in reality there are minor, but important changes.

So without a pic, Wrog would have never spotted that poly cap.

I'm not an expert in area, but I would suggest swapping that out back to an electrolytic.

2 seconds to black could be caused by

1) bad caps
2) ccfl bad or ccfl wiring is bad
3) bad inverter transformer
4) others

See #1, #4, and #5 at

https://www.badcaps.net/forum/showth...+seconds+guide

PS. Rev 0.2 of that document is almost complete. It is revamped quite a bit.

[Jules3084]

Re: Scepter x20wg screen problems

I tried more closely with a flashlight and YES the image from the computer can be seen on the screen with the flashlight.

I order and use poly caps at work for high reliability equipment.
I can't change to a standard cap tonight, but I highly dought that is the problem.

[Jules3084]

Re: Scepter x20wg screen problems

The first time around, I had a standard electrolytic in the C101 position because it was obviously bad with the expanded top. It was replaced with the U101 and U102, the
4511GMs as stated in my earlier post. All the caps were then changed so in the future I wouldn't be dealing with old caps one at a time.

All along the symptoms have been the same.

I'm going to guess that a bad ccfl is shutting down the inverter.

[retiredcaps]

Re: Scepter x20wg screen problems

I order and use poly caps at work for high reliability equipment.
I can't change to a standard cap tonight, but I highly dought that is the problem.

I don't know enough about poly caps to know if they are low ESR or not. PCBONEZ is the expert in this area.

I forgot you already tested the inverter transformer secondaries.

The next step is to see if one of your ccfls are bad or not. Here is where the Hitachi comes into play.

The Hitachi is your good ccfl. Open up the Hitachi. Place it near, but not touching, the Scepter.

Plug in 3 out of 4 ccfl connectors on the Scepter. Plug last remaining cable to the Hitachi. Power on Scepter.

If you observe 2 seconds to black, move onto next ccfl on Scepter and retest. Observe the WAIT ONE MINUTE and POWER OFF warnings in the document.

[jetadm123]

Re: Scepter x20wg screen problems

Hard to ell from the photo, but is the C101 that's currently installed 150uf or 180uf?

[Jules3084]

Re: Scepter x20wg screen problems

In your guide to substitute a spare CCFL in place of an installed one,
what happens if there are two bad CCFLs installed?
Is that possible? Would that change the logic if the problem is more than one CCFL?

[Jules3084]

Re: Scepter x20wg screen problems

C101 is a 150uFD 35V cap.

[retiredcaps]

Re: Scepter x20wg screen problems

In your guide to substitute a spare CCFL in place of an installed one,
what happens if there are two bad CCFLs installed?
Is that possible? Would that change the logic if the problem is more than one CCFL?

It is possible to have 2 bad ccfls. When you go through the tests, if it isn't obvious that 1 ccfl is bad, you can use a similar test, but have 2 known good ccfls.

I'm assuming your Hitachi LCD has at least 2 ccfl connectors. Most LCDs have 4.

BTW, on the Hitachi, you don't actually have to remove the ccfls from the casing. Just stretch the ccfl connector cable from the Scepter close enough to plug into the Hitachi (but not touching to prevent shorting out something).

[Jules3084]

Re: Scepter x20wg screen problems

I'll have to log off now, the Hitachi monitor is my only other monitor.
Please wish me good luck.

Thanks....

[Jules3084]

Re: Scepter x20wg screen problems

I haven't been able to make more progress on this yet, but I do have a question.

If a bad CCFL is determined, is it then that I would determine the size of the replacement?

Also, given 1 out of 4 being bad, should the other three also be replaced?

Thank you,